\begin{tikzpicture}
    \tkzDefPoints{0/0/O, -1.5/0/A, 1.5/0/B, 0/-2/C, 0/2/D, 1.0/1.6/P}

    \tkzDrawSegments(A,B  C,D)
    \tkzMarkRightAngle(B,O,D)
    \tkzLabelSegment[pos=1.0,below](A,B){$a$}
    \tkzLabelSegment[pos=1.0,right](C,D){$b$}
    \tkzDrawPoint(P)
    \tkzLabelPoints[below left](O)
    \tkzLabelPoints[right](P)
\end{tikzpicture}

